In comparison with a filament lamp or fluorescent lamp, SSL lamps demonstrate a significant number of advantages, such as low power consumption, long useful lifetime, smaller size, lighter weight, and being environment friendly. The efficiency of the high brightness LED is higher than that of filament lamps or fluorescent lamps, it has great potential that LED lamp for general illumination will spread widely. However, for such wide spread use to become possible a high efficiency and reliable power controller which converts AC to DC for the SSL driver is desirable.
One LED array usually operates with a few volts of direct-current (DC) power supply voltage, and emits a small amount of illumination. In practical lighting application, an array of a series of LED arrays are connected either in series or in parallel or in combination of series and parallel to achieve a desired illumination flux. In such use the usually commercially available alternating-current (AC) power needs to be converted to direct current (DC); a power supply controller, conventionally, a transformer based AC-DC converter and/or a pulse width modulation (PWM) controller is used for this conversion.
A panel of LED arrays for a lighting application requires high power supply to improve the illumination flux. The LED generally operates at high operating current, i.e. 0.35 A for 1 W LED, 1 A for 3 W LED, 1.5 A for 5 W LED, 3 A for 10 W LED. But the high current and increased power voltage can cause additional thermal dissipation which can significantly decrease the lifetime of a LED lamp. Therefore, enhancing the efficiency of the LED driver to reduce power consumption would be a considerable advantage particularly for general illumination applications.
In a conventional AC-DC converter where a transformer and a PWM method are used, the transformer too consumes power; and the high frequency pulses associated with PWM also generate flashes in SSL illumination which may be detrimental for human eyes and can reduce the lifetime of SSL. Moreover, the power consumption by the power controller itself can increase significantly when operating at high current condition thus rapidly decreasing reliability. In addition, the power efficiency of SSL lighting is lowered if the transformer and PWM power controller are used at high current. The transformer and PWM type of AC-DC converter may only have a typical power efficiency of 70-80%.
Another problem associated with commercial AC power, such as the 220V or 110V system, is that the supplied AC voltage is unstable and can vary around ±20% magnitude. This variation can cause the working current of a SSL lamp change exponentially, thus would significantly affect the lighting intensity of the SSL during the operation of the SSL. The greatly increased current of the SSL could result in reduced SSL lifetime or even damage the device. In addition, high current variation could cause high load variable; temperature, light intensity, transistors, diodes, resistors in the driver circuit become unstable during operation, causing the performance of other electronic devices and LEDs/OLEDs degrade dramatically.
Therefore there is a need for highly efficient, stable and reliable power controller in order for LED/OLED lamp to be used for general illumination applications.